Analog Multimeters: Principles and Usage

• Multimeters are electrical measuring devices used to measure physical quantities like voltage (using as a voltmeter), current (using as an ammeter), and resistance (using as an ohmmeter).
• They can also test for capacitance, diode threshold voltage, continuity, and isolation.
• The two main types of multimeters are digital and analog.

Analog Multimeters

• It's essential to check the batteries, fuses, and test leads before use.
• The reading on analog multimeters is taken via a needle on a scale.
• To measure, the device connects to the parts to be measured using different colored leads fitted with secure contact tips.
• Touching the tips with bare hands can be dangerous due to electrocution risks.

Analog Multimeter Principle

• The analog multimeter works by converting the input signal at its terminals into direct current (DC).
• The resulting current passed through a galvanometer, deflecting a needle on a scale.
• The angle of deflection is proportional to the current and indicated by the needle.
• The galvanometer only accepts low-value direct current and uses a voltage divider to reduce current to that value.
• Alternating current must be rectified before being measured by the galvanometer.
• Circuits containing resistors and generators convert voltage and resistance measurements according to Ohm's law.

The Display

• The readout on an analog multimeter utilizes a scale, either singular or multiple, which indicates what measurement to take.
• Indicators displayed include isolation voltage between terminals, AC/DC, double isolation, horizontal, vertical, and inclined positions. Plus ferromagnetic or Magnetoelectric displays

Characteristics

• Caliber defines the maximum deflection value of the needle, and physical quantity measured.
• The precision of the device increases as the number of calibers increases.
• Range is the maximum deflection without accounting for what could be measured, which can feature on another rotator

Resistance

• The resistance can vary depending on if whether the device is connected in a parallel or series circuit.
• Voltmeters connect in parallel to avoid disturbing the circuit under measurement, internal resistance must be higher than measured element.
• Ammeters connect in series, internal resistance must remain lower than the measured element.

Bandwidth

• Bandwidth is range of frequencies within which the multimeter can be used.
• The reading can be erroneous or absent outside that range.

Advantages

• Primary advantage is to quickly indicate current of voltage change, with needle oscillating
• Commonly used for continuous and isolation tests that dont require a battery

Disadvantages

• Critical to take measures due to needle-based Voltmeters not containing a high enough voltage.
• It can have influence on circuits to measure.
• Results difficult to read as multiple scales

Digital Multimeters

• Digital multimeters show readings on a digital display.
• The batteries, fuses, and test leads must be verified before use.

Conversian and Adapting the Signal

• A digital multimeter relies on voltage and includes current/voltage and ohm/voltage conversions.
• High voltages are reduced before being scaled.
• Low voltages are scaled before range adaptation.

Analog/Digital Conversion Methods

• Analog signal converts to a digital display.
• It can be completed used a CAN dual ramp or a flash converter.

Display

• Displays can be in 7 segments, or crystal

Characteristics

• The number of displayed values determines the resolution.
• The number of decades indicates the number of digits displayed, with a digit able to display 0 to 9.
• A 3-digit display is therefore required to show different values

Caliber and Range

• Caliber and range definitions are similar to those of analog devices, with automatic ranging in digital multimeters.
• The decimal point position depends on the caliber.
• At 1000 points on the 10V caliber, a value between 0.00 and 9.99 is displayed.

Input Impedence

• Entry impedance for this type of meter is generally high and does not disturb circuit operating through voltmeter. Most frequently its equal to 10MΩ

Bandwidth

• Defines the same way it does with multimeters.

Advantages

• It has automatic ranging
• Easy reading

Disadvantages

• Limited bandwidth due to sampling frequencies
• Variation visualization limited to rapid CAN devices.

Clamp Meters

• Clamp meters extend multimeter capabilities, measuring current by clamping around a conductor.

How it Works

• The clamp ammeter measures current using electromagnetic induction, as adjacent to a multimeter
• An effect Hall helps measure intensity using flux proportional to conductor density

Key Feature

• One key advantage of the clamp is the ability to measure without cutting the supply or opening the circuit
• The measuring device is galvanically isolated from he installation.

Electrical Measurement Functions

• multimeters can different types of measures

Measure of voltage

• Measure a continuous alternating voltage
• It is equivalent to a continous voltage for a particular resistance dissipating power

RMS VS TRMS

• Root means square (RMS) is the appellaltion AC.
• True root mean square (TRMS) is the appellation AC+DC, to better real RMS.

Peak and Peak Voltage

• Peak is considered a maximum value, usually determined through a condenser
• Peak to peak provides the overall amplitude of the signal

Current Values

• Current measures can be constant, peak, or efficient.

Ohmic Measures

• Most use to measure resistance
• Requires the pilot battery within

Other Possibilities

• They can also be used to measure other quantities like capacity, diode thresholds, frequencies, etc.

Use and Safety

Safety

• Tests should occur dynamically whilst under tension.
• Connect device when outside for safety, operating after installation
• Some devices have different terminals depending on the intended measurement.

Choice of Terminals

• If used outside the caliber, it may subdue degradation, so should be set to highest caliber
• Analogs need to be tared each caliber use, adjust zero

Measure

• Enables interpreting the physical phenomenon with a measuring device

Voltage Measure

• Adapting device to measure

Choosing Voltage

• Need to know the characteristics of the specified measure:
• DC or AC
• Value effectiveness
• Peal value
• Value estimated

Voltmeter Connection

• To read voltage, set to connect to circuit in parallel

Cold Point Connection

• It has multiple symbols to represent

Mass Floating Equipment

• Point of reference at any point in circuit

Cold Point Equipment

• Reference has to circuit as well

Reading

• After connecting, ensure the circuit is on

Current Measurement

• Caliber must be chosen dependant on expected voltage.

Amperimeter Connection

• It offers a circuit read as circulated.
• To determine circuit, must remain connected in series

Ohmic Measures

• Measure depends on resistance.
• Once measured, must stay isolated from circuit and installed alongside

Continuity, Isolation, etc

• It's important on how to find electrical failure.

Continuity Measure

• This continuity should signify a failure
• Needs apparatus i.e. milliohmeter

Milliohmeter

• Less than Ω in calibre
• Can check air quality
• Currents can be order of amps and is therefore dangerous.
• The generator should be disconnected before disconnecting resistance

Isolation

• To check the connections
• It measures high voltage DC
• Check short circuit indicators

Megohmmeter

• Above 20MΩ
• High voltage and low Amps

Equipment Representation

• Requires extreme precautions
• Test cables against high voltage
• Equipment requires test data before use
• Must ensure equipment isn't touched